Viruses cause a wide variety of diseases in humans ranging from colds and influenza to cancer. Structural studies of the influenza virus haemaglutinin molecule have provided practical insight for understanding the nature and location of antibody binding sites and have revealed the cell receptor binding site. Structural studies of plant viruses have provided fundamental knowledge regarding virus stability, assembly and the structural relationships that exist among plant viruses. We are seeking to answer questions at the fundamental level, concerning the structural relationships among T=3 viruses and their functional implications, as well as specific questions concerning assembly, stability and receptor binding of an insect virus. The goal of the work proposed in this study is the determination of the high resolution structure (3.0 Angstroms of black beetle virus (BBV) using single crystal X-ray diffraction methods. BBV is an isometric RNA virus displaying T=3 quasi-equivalent symmetry. The virus causes fatal paralysis in a variety of Lepedopters and is the subject of intense molecular biological study at the University of Wisconsin, Madison. Until recently only plant viruses have been studied by single crystal X-ray diffranction because of the low yield of animal viruses grown in cell culture. BBV is relatively high yielding virus grown in Drosophila line 1 cells. We seek to answer the following fundamental questions concerning BBV structure, function, and relationship to other viruses. 1) Are all T-3 viruses similar in tertiary and quaternary structure regardless of the kingdom of its host? 2) What are the stabilizing forces in this virus as established by structure and chemistry (the amino acid sequence of the capsid protein is known). 3) What are the driving forces for assembly and disassembly as gleaned from the structure? 4) Are the receptor binding sites of BBV similar to those found in influenza virus haemaglutinin and neuraminidse? 5) How to mutations in the rate of multiplication and plaque forming properties of BBV (known to reside in the capsid protein gene) effect the capsid structure? These studies will be performed with crystals grown at Purdue (P4232 a=352 Angstroms using virus routinely produced at Purdue. The crystals diffract to 3..0 Angstroms resolution. The structure will be determined in two stages (5.0 Angstroms and 3.0 Angstroms using the isomorphous replacement method for initial phasing. The phases will be refined using electron density averaging permitted by the non-crystallographic 5-fold rotational sysmmetry in the crystal.